I have a piccadilly journal that I use for taking notes on self-taught subjects and I have an awkward structure for pagination and page structure:

Page numbers only exist on the right hand side of the page and I read the journal from left to right; however, I read journal entries from right to left (in pages, not words). When a journal entry only spans a single page, I write a new entry on the left side of the journal with the respective date and title on the bottom but I never write new page numbers on the left page.

The journal is now ~56 pages (112 physical pages) and it's becoming difficult to find entries now. I want to list all of the entries in the back as a table of contents or index of some sort but I want to be as space-efficient as possible; how should I do this to be least-redundant (least repetition of page numbers or dates)?

P.S. If I sort them traditionally by pages, some pages will have two entries and others will only have one entry that spans two pages (asymmetrical). If I sort by date, I may have multiple entries per date that spans multiple pages (since I can write more than one journal entry in a day).

You could arbitrarily re-number the pages. Use a prefix like A, start at the lower outside corner of the first page, and call it A1. Your next page, left or right, is A2. Continue to the end. Use that for your TOC/Index.